feat(board): master-task board, non-destructive stall watchdog, review flow

Board is now a clean master-task view:
- GetBoardAsync returns only top-level (master) tasks; child-tasks render
  nested inside their parent card instead of as separate column cards, so a
  big task split into many sub-tasks stays one card (orphans treated as master)
- New DoneChildTaskCount on the DTO for real progress bars
- Child/detail consumers (GetChildren endpoint, TaskBridgeService) query
  children directly instead of scraping the flat board

Stall watchdog (replaces destructive auto-reset):
- StaleTaskRecoveryService.FlagStalledInProgressTasksAsync marks In-progress
  tasks with no activity past the threshold as stalled (activity event +
  Iris notification) WITHOUT resetting the column — no work is discarded.
  Idempotent: a task is not re-flagged until real progress happens
- BackgroundService now runs this watchdog (TaskRecovery:StalledMinutes=40,
  interval 10m); hard reset kept only on the explicit manual endpoint

Review flow (Bao/Iris only):
- POST tasks/{id}/approve (Review -> Done)
- POST tasks/{id}/request-changes (Review -> target, mandatory comment,
  ExpectedFrom=iris, notifies Iris)

Frontend:
- BoardCard component: master card with ball chip (who has it), progress from
  children, expand to show children grouped by agent with per-child state +
  stalled marker, stalled chip on the master, review action buttons
- Request-changes modal; tasks store approveReview/requestChanges actions

Tests: watchdog flag/idempotency + review threshold; 135 backend tests green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/stores/tasks.ts

@@ -30,6 +30,7 @@ export interface DashboardTaskDto {
   lastActivityMessage?: string | null
   lastActivityAt?: string | null
   childTasks?: DashboardTaskDto[] | null
+  doneChildTaskCount?: number
   childTaskCount?: number
   openChildTaskCount?: number
   hasVisibleDelegation?: boolean
@@ -215,6 +216,29 @@ export const useTaskStore = defineStore('tasks', {
       }
     },
 
+    /* ── API: Review abnehmen (Review → Done) ─────── */
+    async approveReview(id: string) {
+      const res = await apiFetch(`/api/dashboard/tasks/${id}/approve`, { method: 'POST' })
+      if (!res.ok) {
+        const body = await res.json().catch(() => ({}))
+        throw new Error(body.error || `HTTP ${res.status}`)
+      }
+      await this.fetchBoard()
+    },
+
+    /* ── API: Änderung anfordern (Review → Zielspalte) ── */
+    async requestChanges(id: string, comment: string, targetState = 'In progress') {
+      const res = await apiFetch(`/api/dashboard/tasks/${id}/request-changes`, {
+        method: 'POST',
+        body: JSON.stringify({ comment, targetState }),
+      })
+      if (!res.ok) {
+        const body = await res.json().catch(() => ({}))
+        throw new Error(body.error || `HTTP ${res.status}`)
+      }
+      await this.fetchBoard()
+    },
+
     /* ── API: Create task ─────────────────────────── */
     async createTask(data: { title: string; detail?: string | null; priority?: string; assignedTo?: string }) {
       try {